1. Field of the Invention
This invention relates to a method for forming phosphors on an interior surface of a faceplate of a display, and more particularly to a method for forming phosphors on an interior surface of a faceplate with barriers defining subpixel volumes.
To optimize the image quality of these displays, it is desirable to construct physical barriers in the boundaries between the color sub-pixels to minimize optical crosstalk between subpixels. These barriers intercept electrons scattered from the phosphor in the case of FED and block diffusion of resonant photons in the case of plasma technology. In both cases, these barriers prevent loss of color purity and contrast. To function as intended, these barriers must be tall. The typical height for both FED and plasma barriers is 50 to 100 .mu.m. This height is relatively independent of the resolution of the display so that as the resolution of the display increases, the pixel size becomes smaller and the ratio of barrier height to pixel width becomes larger.
For both FED and plasma display is it is necessary to form phosphor pixel elements of appropriate thickness and geometry in the wells created by the barriers. For full-color displays it is necessary that the white pixel be composed of adjacent RGB subpixels.
For transmissive displays of the type in which the phosphor screen is deposited on the front or viewing plate, control of the phosphor thickness, density and location is critical for optimum brightness, contrast and color-purity.
Conventional CRT displays generally incorporate a barrier of relatively planar configuration in the boundaries between phosphor subpixels to allow for positional error and to enhance viewing contrast. A common method for phosphor deposition on conventional CRT screens is by first creating a dry film of phosphor of a first color and photosensitive polymer by dispensing a wet phosphor slurry onto a spinning faceplate, drying, exposing the photosensitive film to actinic light through a shadow-mask to create a latent image of the holes in the shadow-mask, followed by developing the unexposed regions to form a phosphor pattern corresponding to the holes in the shadow mask. This process is repeated for phosphor of second and third colors to produce a full-color screen. This process is not hindered by the planar barrier, but results in reduced phosphor adhesion because the phosphor/polymer dot is exposed (and hence polymerized more fully) from the phosphor/air interface rather than from the phosphor/glass interface.
Murakami, et al., Proc. Japan-Korea Joint Symp. Information Display, 1992, pp. 73-78, describe methods for creation of the phosphor pixels by exposure from the glass interface to provide improved adhesion on the front glass of a plasma flat panel. This process requires a complex apparatus including a large (650 mm.times.900 mm) convex lens to create strictly collimated light and uses a large 1:1 photomask to expose the phosphor pattern and (planar) barrier.
Several plasma display designs in which the phosphor pixel is included in the rear plate requires a phosphor picture element geometry with phosphor covering the sides of barrier ribs for brightness efficiency and expose the address (AC plasma) or display-anode (DC plasma) electrode. These designs typically screen-print the phosphor in the deep wells. Since screen printing is an imprecise method for control of thickness and location, the phosphor screened in the wells is typically not of the desired thickness and residual phosphor remains on the tops of the barriers. Therefore, secondary processing is required to remove unwanted phosphor from the barriers and control the thickness in the wells. Sandblasting to remove phosphor is the current art. This is an intrinsically dirty process, subjecting the device to contamination by the blasting media and by the removed material.
These displays are typically "reflective" in which the emitted light from the phosphor (contained on the rear plate) is viewed through a transparent front plate.
From both FED and plasma displays, it is desirable to separate the plate containing the viewing screen (and processes) from the plate containing the emissive elements (and processes). This allows better process control and improves ultimate yield.
Current methods for creating viewing screens with phosphors are costly and difficult to scale to commercial manufacturing process. There is a need for a less expense method to form the phosphor coated viewing screen.